ocfs2: Pass suballocation results back via a structure.

We're going to be adding more info to a suballocator allocation.  Rather
than growing every function in the chain, let's pass a result structure
around.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Tao Ma <tao.ma@oracle.com>

Author: Joel Becker